A crystalline silicon solar cell is a device that effectively absorbs solar radiation energy and converts light energy into electrical energy through the photovoltaic effect.
When sunlight reaches the p-n junction of a semiconductor, new electron-hole pairs are generated. Under the action of the electric field of the p-n junction, the holes flow from the N zone to the P zone, and the electrons flow from the P zone to the N zone, generating current upon switching on a circuit.
In a conventional crystalline silicon solar cell, surface passivation is basically only performed at the front surface, which involves depositing a layer of silicon nitride on the front surface of the silicon wafer via PECVD to reduce the recombination rate of the minority carriers at the front surface. As a result, the open-circuit voltage and short-circuit current of the crystalline silicon cell can be greatly increased, which leads to an increase of the photoelectric conversion efficiency of the crystalline silicon solar cell. However, as passivation is not provided at the rear surface of the silicon wafer, the increase in photoelectric conversion efficiency is still limited.
The structure of an existing bifacial solar cell is as follows: the substrate is an N-type silicon wafer; when photons from the sun reach the rear surface of the cell, the carriers generated in the N-type silicon wafer pass through the silicon wafer, which has a thickness of about 200 μm; as in an N-type silicon wafer, the minority carriers have a long lifetime and carrier recombination rate is low, some carriers are able to reach the p-n junction at the front surface; the front surface of the solar cell is the main light-receiving surface, and its conversion efficiency accounts for a high proportion of the conversion efficiency of the whole cell; as a result of overall actions at both the front surface and the rear surface, the conversion efficiency of the cell is significantly increased. However, the price of an N-type silicon wafer is high, and the process of manufacturing a bifacial N-type cell is complicated. Therefore, a hotspot for enterprises and researchers is to how to develop a bifacial solar cell with high efficiency and low cost.
On the other hand, in order to meet the ever-rising requirements for the photoelectric conversion efficiency of crystalline silicon cells, the industry has been researching rear-surface passivation techniques for PERC solar cells. Mainstream manufacturers in the industry are mainly developing monofacial PERC solar cells. The present invention combines a highly efficient PERC cell and a bifacial cell to develop a bifacial PERC solar cell that has overall higher photoelectric conversion efficiency.
Bifacial PERC solar cells have higher usage values in the practical applications as they have high photoelectric conversion efficiency while they absorb solar energy on both sides to generate more power. Thus, the present invention aims to provide a bifacial P-type PERC solar cell which is simple to manufacture, low in cost, easy to popularize, and has a high photoelectric conversion efficiency.